Automated data storage libraries provide a means for storing large quantities of data in portable data storage media, such as magnetic tape cartridges, optical disk cartridges, etc., that are stored in a readily available form at storage shelves of the library. The portable data storage media are accessed and transported with respect to the storage shelves and at least one data storage drive by an accessor, and the data storage drive(s) transfer data with respect to the portable data storage media.
Typically, data stored at portable data storage media of an automated data storage library, once requested, is needed quickly. Thus, it is desirable that an automated data storage library continue to be in operational condition as much as possible, such as the well known “24×7×365” availability. If only a single accessor is supported, an error to operation of the accessor can cause customer downtime. Hence, the addition of another accessor will aid in reducing customer downtime and impact. The accessors typically operate on the same path to serve the entire library on the one path, and can work in a “hot standby” configuration, or in a “dual active” or “multiple active” configuration. In a hot standby configuration, only one accessor is active at any single time, and another accessor is in standby mode, waiting for an operational failure to occur on the active accessor. Thus, the standby accessor would only take over in the event of a failure of the active accessor, and the standby accessor may push the active accessor into a service bay, and would become the active accessor. Examples of active/standby accessors comprise U.S. Pat. No. 5,894,461 and U.S. Pat. No. 6,309,162. In a multiple active configuration, both of the accessors are active, and move within separate virtual libraries, or sections of the automated data storage library, which may overlap. In the event of a failure of one of the accessors, another accessor would push the failed accessor into a service bay, and would take over for the entire automated data storage library. An example of multiple active accessors comprises U.S. Pat. No. 6,304,524.
A key element in reducing customer downtime and impact is to clear the aisle or accessor path in the event of an accessor failure so that the library is fully functional and to allow the other accessor full access to the whole library. Therefore, if the failing accessor is unable to move out of the path, another accessor must try to push the failing accessor into a service bay, so that the another accessor will have full access to the whole library, which eliminates customer downtime. However, there are certain scenarios where failures can halt the library. An example of an error that causes customer downtime is if there is a stuck portable data storage media cartridge between the accessor and a drive or storage shelf. Another example is if a cartridge has been dropped and is blocking the accessor along the path. The path is typically a rail, and the cartridge may jam between the accessor and the rail. In each example, the accessor is failed due to the stuck or jammed cartridge, and it may not be possible to move the failed accessor, halting the operation of the library.